Use of materials as waterflood additives

ABSTRACT

One embodiment includes an oil recovery process, more particularly a secondary or tertiary type crude oil recovery process utilizing a drive fluid to move a displacing fluid through a subterranean formation wherein the displacing fluid displaces crude oil therefrom and is driven through the formation by means of the drive fluid. The crude oil recovery process is improved by utilizing as the drive fluid a thickened, transparent, aqueous solution of a water-soluble sulfated, polyethoxylated C10-C18 primary alcohol or alkylated phenol. The displacing fluid is generally an aqueous surfactant solution, a miscible displacing medium or most preferably a microemulsion. In a further embodiment, the water-soluble, polyethoxylated C10-C18 primary alcohol or alkylated phenol is employed as a mobility control agent in a waterflood thereby increasing the sweep efficiency thereof.

United States Patent Gale et al.

[ USE OF MATERIALS AS WATERFLOOD ADDITIVES [75] Inventors: Walter W.Gale, Houston; Thomas L. Ashcraft, .lr.; Rhoderick K. Saunders, both ofBaytown, all of Tex.

[73] Assignee: Exxon Production Research Company, Houston, Tex.

{22] Filed: Jan. 2, 1974 [21] Appl. No.: 430,330

[ June 10, 1975 Primary Examiner-Stephen J. Novosad AssistantExaminer-George A. Suckfield Attorney, Agent, or Firm-Lewis H. Eatherton[57] ABSTRACT One embodiment includes an oil recovery process, moreparticularly a secondary or tertiary type crude oil recovery processutilizing a drive fluid to move a displacing fluid through asubterranean formation wherein the displacing fluid displaces crude oiltherefrom and is driven through the formation by means of the drivefluid. The crude oil recovery process is im proved by utilizing as thedrive fluid a thickened, transparent, aqueous solution of awater-soluble sulfated, polyethoxylated C -C primary alcohol oralkylated phenol. The displacing fluid is generally an aqueoussurfactant solution, a miscible displacing medium or most preferably amicroemulsion. In a further embodiment, the water-soluble,polyethoxylated C,,,C primary alcohol or alkylated phenol is employed asa mobility control agent in a waterflood thereby increasing the sweepefficiency thereof.

25 Claims, 2 Drawing Figures BRINE OIL USE OF MATERIALS AS WATERFLOODADDITIVES BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates in one embodiment to a method of recovering crude oilfrom subterranean formations wherein a displacing fluid is injected intothe formation through at least one injection means to displace crude oiland is driven by means of a drive fluid toward at least one productionmeans; more specifically, this invention in that embodiment relates to asecondary and/or tertiary recovery method for recovering crude oil froma subterranean formation wherein an improved drive fluid is employed todrive through the formation a displacing fluid capable of displacing thecrude oil in the formation to the production means. In a furtherembodiment of the present invention a waterflood of improved sweepefficiency is provided through the use of a specific mobility controlagent.

2. Description of the Prior Art Knowledge is widespread in the oilindustry that the so-called primary recovery techniques, which includenatural flow, gas lifting, gas repressurization and pumping methods,leave substantial quantities of oil in oil-bearing reservoirs.Recognition of the large amount of oil remaining in many oil-producingreservoirs has led to the use of so-called secondary and tertiaryrecovery" techniques which have as their primary purpose the economicalrecovery of additional quantities of the oil known to be present in thereservoir.

Probably one of the more common secondary recovery techniques is theso-called waterflooding" in which aqueous fluids are injected at one ormore points in the reservoir at pressures sufficient to force the fluidsout into the reservoir and toward a spaced production well or wells.This, in effect, displaces oil from the pores of the reservoir anddrives the oil ahead of the water front.

However, such techniques, e.g. waterflooding, are only advantageous whenthe cost of injecting water and necessary chemical modifiers is lessthan the value of the oil recovered. As a result the displacementefficiency of waterflood or the like has been the determining factor ofwhether such a technique will be used.

Generally, the difficulty with waterfloods is that the small pores andcapillaries of the reservoir contain hydrocarbons (oil and/or oil andgas) which are generally water immiscible. The existence of highinterfacial tensions between the boundary of the water and hydrocarbonsseriously impedes the ability of the Water to displace oil trapped inthe reservoir by capillarity.

Since in many oil-bearing reservoirs the oil tends to be trapped withinthe pores of the rock formations by capillarity, merely forcing watertherethrough will not displace this trapped oil. However, a sufiicientreduction in the interfacial tension between the water and the oil willincrease the amount of oil that will be displaced by the water. Thus,various aqueous surfactant systems have been proposed for use inwaterflooding processes for recovering oil, the surfactants having theability to reduce the interfacial tension between the oil and water.

Many aqueous systems containing surfactants have also been proposed inwhich the effective oil recovery is improved by treating the formationwith a liquid which contains an oil-solubilizing, aqueous solution ofsurfactant micelles that are combined with molecules of an amphiphilicorganic compound of low water solubility; the amphiphilic material beingcapable of swelling the surfactant micelles and causing the aqueoussolution to solubilize a significant proportion of oil. In using suchsystems oil is recovered by injecting an aqueous liquid to drive thesurfactant system and the oil towards the production means.

A fluid which has been used in secondary and tertiary oil recovery isone which employs a solvent that is miscible with both the connate oiland with the flood water. This fluid is introduced into the formationahead of the flood water. Alcohols and various other organic solventshave been proposed as suitable miscible agents for use in the so-calledmiscible flooding operation. Methods utilizing hydrocarbons as misciblefluids are extremely successful with regard to the displacementefficiency of the crude oil, particularly the ability to displaceessentially all of the crude oil from the formation contacted. However,the volumetric sweep efficiency of these flooding media is adisadvantage. The hydrocarbons inherently finger and channel to a greatextent and a large portion of the reservoir is bypassed although thevolume of injected hydrocarbons may be great. This is economicallydisadvantageous.

A typical miscible flooding process is the miscible slug process. Thisis a process which consists of injecting a limited quantity of fluid,e.g. propane, LPG, or similar solvent, into an oil reservoir and pushingthis liquid bank toward producing wells with another fluid injectedsubsequently. The injected fluid being miscible with reservoir oilresults in efficient displacement of the oil.

More recently, attention has turned toward the injection of amicroemulsion in the form of a microemulsion slug. Such microemulsioncan be defined as a stable transparent or translucent micellar solutionof oil and water that may contain one or more electrolytes, and asurfactant, optionally containing one or more cosurfactants. The oil,water and surfactant are essential components of the microemulsion withthe surfactant being present in an amount greater than the criticalmicelle concentration so as to form the desired microemulsion. Themicroemulsion can be a water-external microemulsion, an oil-externalmicroemulsion or a microemulsion in which there is no discernibleexternal phase.

Regardless of the type of displacing fluid which is employed in thesecondary and/or tertiary recovery process, one or more slugs of thedisplacing fluid are driven through the formation by means of a drivingfluid. To eliminate a fingering effect of the displacing fluid slugthrough the formation, the displacing fluid slug is generally providedwith a mobility control agent. Likewise, in order to eliminate anunwarranted fingering effect between the displacing fluid and drivefluid, it has been proposed to thicken the drive fluid so that themobility of the drive fluid is substantially equal to or less than themobility of the displacing fluid slug.

Various materials have been proposed for use as thickening agents ormobility control agents to increase the viscosity of the flood water.Such materials include fatty acid soaps, alginates, sucrose, dextran,amines, glycerine, and a number of water-soluble polymers. The materialswhich have been found commercially satisfactory fall into two generalcategories, the first being the natural polymers such as polysaccharideswith the second being a class of polyacrylamides, specifically partiallyhydrolyzed polyacrylamides. Commercially available thickeners fallingwithin the foregoing groups include a material sold by Kelco Industriesunder the name ofl(elzan XC," a polysaccharide, and materials sold bythe Dow Chemical under the name Pusher, a partially hydrolyzedpolyacrylamide. While these materials are effective in thickening theaqueous flood and decreasing the mobility thereof, they have certainserious drawbacks, particularly when utilized to drive a microemulsionslug and in waterflood applications.

For example, the polysaccharides, while showing sufficient thickeningcharacteristics, have the disadvantage of poor filtrationcharacteristics; particularly in saline water. The polyacrylamidematerials are also disadvantageous in that they show permanent sheardegradation effects even at low shear rates. Materials of the foregoingtypes, cannot be advantageously employed as driving fluids formicroemulsion slugs since both types of material show very poor phasebehavior with microemulsions, the microemulsions quickly breaking downinto multiphase systems, thereby shortening the efficient miscibledisplacement of single phase microemulsions. Accordingly, the art haslong sought a drive fluid which can be effectively employed with alltypically employed displacing fluids which eliminates the disadvantagesof the materials proposed heretofore.

SUMMARY OF THE INVENTION It has been discovered in accordance with thepresent invention that the foregoing disadvantages can be eliminated andan improved process for recovering crude oil can be provided in oneembodiment by injecting into the formation at least one displacing fluidand driving such displacing fluid through the formation by means of anaqueous driving fluid comprising a thickened, transparent, aqueoussolution of a water-soluble sulfated, polyethoxylated C -C alcohol, e.g.primary alcohol or alkyl phenol. In this regard it has been discoveredthat the use of such driving fluid eliminates the fingering anddegradation disadvantages and demonstrates good phase behavior,particularly when driving a microemulsion slug through the subterraneanformation. Still further, it has been discovered that the use of thespecific materials enumerated above and illustrated hereinbelow providesa thickening effect at least comparable in cost per centipoise to thematerials commercially available thus providing an economical drivefluid. Accordingly through the foregoing an advantageous process for therecovery of crude oil from a subterranean formation has been developed,such process being particularly applicable in secondary and tertiaryrecovery.

In a further embodiment of the present invention an improved waterfloodis provided by utilization of a thickened, transparent, aqueous solutionof a watersoluble, sulfated polyethoxylated C -C alcohol, e.g., primaryalcohol or alkylated phenol, ahead of the waterflood thereby increasingthe sweep efficiency of the waterflood and increasing oil production,not by surfactant action but through the provision of a more favorablemobility and sweep of the reservoir.

Therefore it is a primary object of the present invention to provide aprocess for the recovery of crude oil from a subterranean formationwherein a displacing fluid is injected into the formation through atleast one injection means and the displacing fluid is driven through theformation by means of a drive fluid, wherein such process eliminates theinherent disadvantages and deficiencies of previously proposedprocesses.

It is a further object of the present IHVT"TIlOfl to provide an improvedprocess for the recovery of oil from a subterranean formation byinjecting into such formation at least one displacing fluid and drivingthe displacing fluid through the formation by means of a driving fluidcomprising a thickened, transparent, aqueous solution of a water-solublesulfated, polyethoxylated C C primary alcohol or alkylated phenol.

It is yet a further object of the present invention to provide suchimproved process for the recovery of crude oil from a subterraneanformation wherein the driving fluid comprises a thickened, transparent,aqueous solution of a water-soluble, sulfated, polyethoxylated C Cprimary alcohol or alkylated phenol, in an amount sufficient to reducethe mobility of the driving fluid and increase the production of thecrude oil.

It is yet a further object of the present invention to provide suchprocess in which the displacing fluid is a microemulsion slug and thepoor phase behavior associated with conventional driving fluids iseliminated by use of a driving fluid comprising a thickened transparentaqueous solution of a water-soluble, sulfated polyethoxylated C -Cprimary alcohol or alkylated phenol.

It is yet a further object of the present invention to provide animproved waterflood process in which the sweep efficiency of thewaterflood is improved through the injection of a slug of an aqueoussolution of a watersoluble sulfated polyethoxylated C C primary alcoholor alkylated phenol ahead of the waterflood.

Still further objects and advantages of the process of the presentinvention will be apparent from the following more detailed descriptionthereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ternary diagram of amicroemulsion system illustrating superior phase behavior associatedwith the water-soluble, sulfated polyethoxylated alcohols of the presentinvention when compared with commercially available thickeners; and

FIG. 2 is a plot of viscosity versus concentration illustrating theviscosity increase effect in accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT The process of the present inventionis applicable to all phases of crude oil recovery; however, the processis particularly adapted for secondary and tertiary recovery.Accordingly, the description hereinabove and the description whichfollows is presented by embrace not only secondary and tertiary recoveryof oil but any and all waterflooding processes and processes in which adriving fluid is utilized to drive a displacing fluid which is injectedinto the formation through at least one injection means and whichdisplaces crude oil toward at least one production means.

One embodiment of the process is applicable to driv ing any and allslugs which are introduced into the formation for the purpose ofdisplacing crude oil. Accordingly, the process of the present inventionfinds application in driving aqueous surfactant slugs which, aspreviously indicated, optionally contain an amphiphilic material of lowwater solubility so as to enhance the displacement associated with theemployment of the aqueous surfactant system. Still further the processfinds application in those recovery techniques in which a slug of amiscible solvent is employed to provide a miscible displacement of thecrude oil within the formation. As indicated above however the processof the present invention has particular applicability in driving a slugof microemulsion since an advantageous characteristic of the presentinvention, not associated with previously employed systems, involves theunexpectedly superior phase behavior associated with the specificmaterials of the present invention and microemulsion slugs.

The displacing fluids applicable in accordance with the presentinvention are well known in connection with techniques for recoveringcrude oil. For exampie surfactants employed in the aqueous surfactantsystem can be any of the anionic, nonionic, or cationic types as well asmixtures thereof. Similarly the miscible displacement fluids aregenerally comprised of semipolar, organic compounds such as alcohols,ketones, esters, etc. and/or hydrocarbons as well as other known agentsmiscible with the formation crude, with the microemulsions being stable,transparent or translucent micellar solutions of oil, water, andsurfactant, optionally containing one or more electrolytes and/orcosurfactants. Any type of microemulsion is applicable, it being notedthat two of the criteria for successful microemulsion flooding are aminimization of the multiphase region and low interfacial tension in themultiphase region eventually reached by breakdown of the single-phasemicroemulsion by dilution with formation water, oil, and drive fluidthereby turning effective miscible displacement into the less effectiveimmiscible displacement. Again any displacing fluid which can beutilized for displacing and recovering crude oil can be advantageouslyemployed in the process of the present invention.

Generally, the displacing fluid viscosity is controlled so as toeliminate an undesirable fingering" of the displacing fluid through theformation. Likewise, to achieve the objects and advantages of thepresent invention, the viscosity of the driving fluid utilized to drivethe displacing fluid slug or slugs through the formation, should besubstantially equal to or greater than that of the displacing fluid soas to eliminate unwarranted fingering effects. These objects andadvantages are achieved by employing in the driving fluid awatersoluble, sulfated, polyethoxylated C -C alcohol or alkyl phenolwhich provides a transparent, singlephase, aqueous driving fluid whichcan effectively promote crude oil recovery by allowing the displacingfluid to displace the crude oil without any of the disadvantagesinherent in systems previously utilized.

The materials utilized to effectively reduce water mobility behinddisplacing fluid slugs are water-soluble, sulfated, polyethoxylated C -Calcohols, more specifically water-soluble, sulfated, polyethoxylated C-C primary alcohols and alkyl phenols.

Typical ethoxylated alcohols are available commercially from ShellChemical Company under the trade name Neodol or from Conoco under thename Alfol" and others. A typical Neodol identified as Neodol 23-6.5which is a mixture of C r-C alcohol having an average of 6.5 (B0)ethoxylate groups has the properties shown in Table l.

Other typical ethoxylated alcohols are shown in Table 2 and have thefollowing properties where E0 is radical.

TABLE 2 Ethoxylates CPI-C15 lr lfi C|2 C!5 Analyses 3 B0 7.5 B0 9 E0Ash, percent 0.2 max 0.0] max 0.01 max Color, APHA 100 max max 75 maxpH, 1% Solution 5.5-6.5 Within 0.5 Within 05 water used water used Acidvalue, 0.004 max 0.0003 max 0.0003 max eqJlOO g.

Conoco Alfol alcohols such as Alfonic" 1012-6 or 1218-6 have thestructural formula:

where x is 8-16 and n 5.8.

Thus, Alfonic 1012-6 is a C primary alcohol containing 6 ethylene oxideunits and 1218-6 is a C primary alcohol containing 6 ethylene oxideunits.

The ethoxylated alcohols can be easily sulfated by reacting theethoxylated alcohol with chlorosulfonic acid or any other conventionalsulfating agent. Sulfated ethoxylated alcohols are also commerciallyavailable materials, for example, by Shell Chemical Company under thetrade name Neodol 23-3A having the following formula:

C O(CH CH O) SO;,NH, and Neodol 25-38 having the following formula:

C|2 |5O(CHQCHZO)3SO3NH The foregoing sulfated, ethoxylated alcohols havethe following properties:

TABLE 3-Continued Typical Physical and Chemical Properties of NeodolsNeodol Ethoxysulfates Analyses 23-3A 25-38 Inorganic salt,

percent weight L 1.0 Odor Mild Mild pH 7.3 7.7

Other anionic, sulfated, ethoxylated alcohols are available from UnionCarbide under the trade name Tergitol S," which have the propertiesshown in Table TABLE 4 Tergitol Anionic Property l5-S-3A -5-35 alltylcarbon range it H lt t5 Average moles of ethylene oxide 3 3 Activecontent,

Composition: ethoxysulfate Cation. ammonium Cation: sodium l0 percentsolution in water; Klett-Summerson units Determined on a 2% aqueoussolution Determined by ASTM Method D I310 using Tag open cup Any and allof the foregoing water-soluble, sulfated, polyethoxylated alcohols canbe employed in accordance with the present invention, the alcohols beingprimary alcohols or alkyl phenols. In this regard ethoxylated materialssuch as polyethoxylated alkyl phenols, specifically octyl and nonylphenols, are commercially available under the trade name Triton X-l00.Similarly the well known sulfated polyoxyalkylated glycols, esters, andethers may be employed to increase the viscosity of the aqueous floodand to reduce water mobility behind aqueous surfactant, microemulsionand miscible slugs, etc.

In the preferred embodiment of the present invention, the water-soluble,sulfated, polyethoxylated C -C alcohol is a sodium sulfate of apolyethoxylated C o-C18 primary alcohol with the product sold under thename Neodol -35" being a representative example. This material is one inwhich an average of three ethylene oxide groups are attached to themolecule. Of course, greater or lesser amounts of ethylene oxide can beattached and the present invention finds application in the use of thosewatersoluble, sulfated materials which contain from 1 to about 100 molesand preferably l to about l0 moles of ethylene oxide per mole ofcompound. Still further, those sulfates which have from 10 to 18 carbonatoms are applicable with those from 12 to l5 carbon atoms being mostpreferred. In this regard it has been discovered that the selection ofany particular material for any specific use can be easily de terminedthrough routine experimentation. By changing the carbon content and/orethylene oxide content based upon the salinity of the aqueous flood, itis possible to achieve optimum viscosity and optimum mobility for theaqueous flood behind the displacing fluid slug. Thus, it has beendiscovered that to accommodate a higher salinity it is merely necessaryto increase the ethylene oxide content or decrease the carbon chainlength within the limits set forth above. Again, the selection of anyparticular material within the foregoing limits to achieve the objectsand advantages of the present invention can be easily carried out.

The selection of materials for use in secondary and tertiary recovery isalways governed by economics since the value of recovered crude oil mustbe greater than the cost of materials utilized. Accordingly, the cost ofmaterials is a factor which must be seriously considered in thedevelopment of any process for the displacement of crude oil andrecovery of the same through secondary and tertiary techniques. Theprocess of the present invention compares favorably with thecommercially available materials and processes since it has beendetermined that the cost per centipoise of the water-soluble, sulfated,polyethoxylated alcohol employed in accordance with the presentinvention is no greater than that of the commercially availableproducts.

An adequate increase in viscosity and associated decrease in mobility ofthe aqueous flood behind the dis placing fluid slug can be achieved byutilizing up to about 1.5% of the water-soluble, sulfated,polyethoxylated alcohol or alkyl phenol based on the weight of theaqueous flood. No lower limit for the amount of the sulfate exists andin actuality it should be the smallest amount possible governed by theresults which provide the desired increase in viscosity and the desireddecrease in mobility. Although the maximum of 1.5% is set forth above,it should be recognized that this upper limit is for economic reasonsprimarily and the watersoluble, sulfated, polyethoxylated alcohol can beemployed in slightly greater amounts to achieve specific results.

The drive fluid employed in accordance with the present invention is atransparent, aqueous solution of the water-soluble, sulfated,polyethoxylated alcohol or alkyl phenol. In this regard it is importantthat a multiphase system not be present but that a transparent,single-phase, aqueous solution be utilized as the drive fluid. Moreover,since the water-soluble, sulfated, polyethoxylated alcohol or alkylphenol is not subject to limitations based upon salinity, the salinitycan vary within wide limits. In this regard the process of the presentinvention finds particular applicability in high salinity environments,i.e., salinities of 2% ,or more, where other conventionally utilizedmaterials encounter difficulties when used. Moreover, since thewatersoluble, sulfated, polyethoxylated alcohol or alkyl phenol iscompatible with the ions normally present in the formation, the presenceof divalent calcium and magnesium ions does not adversely affect theobjects and advantages which are achieved through the use of the drivefluid in the process of the present invention. Similarly, problems ofpoor filtration and degradation are completely avoided.

It should be apparent that the percent formation pore volume ofdisplacing fluid utilized in the process of the present inventiondepends among other factors, upon the crude oil, the formation, and thetype of displacing fluid slug utilized. While the drive is true, ingeneral practice the displacing fluid slug is employed in an amount fromabout 1% to about 40% or more formation pore volume to displace thecrude oil. Also, the pore volume of the driving fluid is not subject toany particular limitations and amounts less than, equal to, or greaterthan 100% pore volume can be advantageously employed. The drive fluid isemployed in an amount sufficient to drive the displacing fluid throughthe formation, thereby displacing the crude oil and driving the sametoward the production means. Volumes typical in the environment of thepresent invention, e.g. from about 10% to about 60% PV or more, can beused without limitation.

1n the typical embodiment employing the process of the present inventionone or more displacing fluid slugs is injected into the subterraneanformation through one or more injection wells spaced apart from one ormore production wells. The displacing fluid slugs are driven byinjecting the aqueous flood drive fluid containing the water-soluble,sulfated, polyethoxylated, alcohol or alkyl phenol in accordance withthe present invention. The displacing fluid slugs displace the crude oiltoward the production wells wherein the crude oil is withdrawn to thesurface of the earth. Accordingly, in the preferred embodiment of thepresent invention one or more injection wells are in communication withone or more production wells through the subterranean for mation. Whilethis is the case, it should be readily apparent that the process of thepresent invention is also applicable to a system wherein the same wellacts both as the injection well and production well in a pushpull" typeof operation. Accordingly, the description set forth above is deemed toembrace this type of operation as well as the conventional operationemploying one or more injection wells spaced from one or more productionwells.

As indicated previously, the process of the present invention findsgreat application with regard to driving a microemulsion slug employedin secondary or tertiary crude oil recovery. The application of theprocess of the present invention to the foregoing environment is basedupon the fact that the transparent, aqueous drive solution shows afavorable phase behavior with the microemulsion slug. In this respectprevious drive solutions containing natural and synthetic polymericthickeners have been unsatisfactory with respect to microemulsion slugssince the phase behavior is quite poor and the microemulsion readilybreaks down to a multiphase system in the presence of the thickeningagent. Reference to FIG. 1 will readily explain the unexpectedsuperiority of the drive solution containing the Watersoluble, sulfated,polyethoxylated alcohol when compared With conventionally employedthickeners such as polysaccharides or partially hydrolyzedpolyacrylamides.

In FIG. 1 four curves are set forth in order to compare the phasebehavior of the water-soluble, sulfated polyethoxylated alcohol of thepresent invention with respect to microemulsions and the phase behaviorof the commercially available Kelzan XC and Dow Pusher. It should benoted in reference to FIG. 1 that the ability of a microemulsion toeffectively displace crude oil in a subterranean formation is dependentupon a minimization of the multiphase region and a low interfacialtension in this region since in the single phase region the displacementof the crude oil is miscible and substantially all of the oil can berecovered and upon breakdown of the microemulsion into the multiphaseregion, the displacement of the crude oil becomes immiscible and aportion of the oil remains trapped in the pores of the subterraneanformation. Accordingly, for a drive fluid to be effective, the same mustnot only possess the appropriate mobility ratio with the microemulsionslug, but in addition the phase behavior of the microemulsion in thepresence of the drive fluid must be such that breakdown of the singlephase microemulsion into the multiphase region must not be accelerated.

Turning to FIG. 1, curve A represents the binodal curve developed for awater-oil-surfactant system wherein the water is high salinity TarSprings Brine (approximately l00,000 ppm dissolved solids). The oil wasa /10 Isopar-M/Heavy Aromatic Naphtha (HAN) mixture, Isopar-M and HeavyAromatic Naphtha being tradenames for refined paraffinic and aromaticoils respectively sold by Exxon Company, U.S.A. and the surfactant wasan 86.2% active mixture of a monoethanolamine C orthoxylene sulfonateand a sulfate of a C phenol containing approximately 13 moles ofethylene oxide, the sulfate being present in the surfactant system toprovide increased brine tolerance for the monoethanolamine C orthoxylenesulfonate so as to allow an effective comparison of the thickener in thehigh salinity Tar Springs Brine. For purposes of reference it is notedthat with regard to the binodal curve representing this control examplewithout any added thickener, the area above binodal curve A representsthe single phase region with the area below the binodal curverepresenting the multiphase region. For purposes of an effectivemicroemulsion flooding procedure minimization of the multiphase regionis desired so that miscible displacement of the crude oil can take placefor a longer period of time.

Binodal curve B represents an embodiment with the scope of the presentinvention wherein the Tar Springs Brine contains 1.5% of a watersoluble,sulfated polyethoxylated alcohol, in this case a sulfate ofa C alcoholcontaining approximately 4.7 moles of ethylene oxide. The watersoluble,sulfated, polyethoxylated alcohol was employed in the Tar Springs Brinein an amount of 1.5%. It is noted when comparing Binodal curve B withBinodal curve A that when utilizing this water thickener the area of theternary diagram below the binodal curve, i.e., the multiphase region,has in fact been reduced. This therefore illustrates the effective phasebehavior associated with the water-soluble, sulfated, polyethoxylatedalcohol of the present invention when employed in combination with themicroemulsion.

Curve C represents the binodal curve for an embodiment outside the scopeof the present invention utilizing 750 ppm Kelzan XC in the Tar SpringsBrine. It can be observed that the multiphase region in the ternarydiagram has been greatly increased and in fact an area exists in whichthe single phase region could not be observed (denoted with dottedlines). This feature associated with the binodal curve when Kelzan XC isemployed in the brine and the increase in the multiphase region of theternary diagram with the resulting decrease in the single phase regionindicate the poor phase behavior of the Kelzan XC with the microemulsionand indicates that an early breakdown of a microemulsion into themultiphase region will occur when Kelzan XC is employed as a thickeningagent or mobility control agent in a drive fluid. Accordingly, binodalcurve C illustrates the disadvantageous characteristics of Kelzan XC inthe environment of the present invention, specifically in connectionwith the employment of microemulsions in the recovery of crude oil.

The last curve in the Figure, curve D, represents the binodal curvewherein 750 ppm Dow Pusher was introduced into the Tar Springs Brine.Here again, as was the case with regard to curve C, it is noted that thearea below the binodal curve, i.e., the multiphase region, is greatlyincreased with the corresponding decrease in the single phase region anda similar area exists in which the single phase region cannot beappropriately identified. This therefore establishes the poor phasebehavior associated with Dow Pusher and microemulsion systems such thatthe microemulsion would tend to break down earlier into the multiphaseregion in the presence of the Dow Pusher thereby illustrating theineffectiveness of this thickener or mobility control agent in a drivefluid associated with microemulsion utilized for the recovery of crudeoil.

It is noted that the compositions utilized to prepare binodal curves Cand D contained the Kelzan XC and Dow Pusher in amounts less thanwatersoluble sulfated, polyethoxylated alcohol utilized in thecomposition in the preparation of binodal curve B. The use of evengreater amounts of the Kelzan XC and Dow Pusher will produce evenfurther adverse effects such that a true comparison between thethickener or mobility control agent of the present invention and thoseof the prior art is made through the foregoing. However, as indicatedpreviously, due to the lower cost of the water-soluble, sulfated,polyethoxylated alcohols when compared with conventionally employedthickeners or mobility control agents, the thickening effect achieved inaccordance with the present invention on a cost per centipoise basis isequivalent to the conventionally employed thickeners. Accordingly, theimproved phase behavior associated with the water-soluble, sulfated,polyethoxylated alcohols or alkyl phenols of the present invention whencompared with the conventionally employed materials is an advantagewhich illustrates the superiority of the present invention over the useof commercially available materials.

While the foregoing discussion deals primarily with the employment ofthe aqueous solution of the watersoluble, sulfated, polyethoxylated C -C15 alcohol, e. g., primary alcohol or alkylated phenol, as a drivingfluid to drive a displacing fluid through a subterranean formation, afurther embodiment of the present invention, an improved waterflood, isprovided by utilizing a thickened, transparent, aqueous solution of awatersoluble, sulfated, polyethoxylated C -C alcohol ahead of thewater-flood, thereby increasing the sweep efficiency of the watertlood,increasing oil production not by surfactant action but through theprovision of a more favorable mobility and sweep of the reservoir. Whenutilized in this manner, the thickened, transparent, aqueous solutionwill be injected into the subterranean formation as a slug prior to thewaterflood, thereby increasing the oil production which can be achievedthrough the waterflooding operation. Generally the volume of theinjected slug of thickened, transparent, aqueous solution will be fromabout 10% to 60% pore volume with the waterflooding being injected ingreater amounts to recover the crude oil trapped within the subterraneanformation. Accordingly, the utilization of the thickened, transparent,aqueous solution of the water-soluble, sulfated, :3:.xylated C -Calcohol in this environment constitutes a further improvement associatedwith the present invention.

The method of the present invention will now be described by referenceto the following examples. It is to be understood that such examples arepresented for purposes of illustration only and the present inventioncannot under any circumstances be deemed limited thereby.

EXAMPLE 1 This example was conducted in order to demonstrate theviscosity increasing ability of various water-soluble, sulfated,polyethoxylated alcohols within the scope of the present invention. Inthis experiment the viscosity of solutions of the water-soluble,sulfated, polyethoxylated alcohols was investigated as a function ofsurfactant concentration and structure, with each viscosity beingdetermined in a capillary viscometer at l00F using 100% Tar SpringsBrine as the dispersing medium. The compounds investigated were asfollows:

FIG. 2 plots the viscosity in centipoise versus the concentration ofsurfactant in weight percent. It can be seen from FIG. 2 that all of thewater-soluble, sulfated, polyethoxylated alcohols enumerated aboveshowed a substantial viscosity increasing ability in the high salinitybrine. Based upon the low cost of the water-soluble, sulfated,polyethoxylated alcohols it can be determined from the viscosityincrease data above that a viscosity increase in cost per centipoise ofthe water'soluble, sulfated, polyethoxylated alcohols is at leastequivalent to the commercially available Kelzan XC and Dow Pusher.

COMPARATIVE EXAMPLE 1 AND EXAMPLE 2 The effectiveness of thewater-soluble, sulfated polyethoxylated, alcohol in a driving fluid todrive a high salinity microemulsion when compared with a similar drivingfluid containing Kelzan XC can be readily seen in this ComparativeExample 1 and Example 2 carried out in accordance with the presentinvention.

The microemulsion employed was one comprising 40.4% Tar Springs Brine,47.0% of an oil, a /10 [50- par-M/HAN mixture, 4.1% of the surfactantmonoethanolamine C orthoxylene sulfonate, 5.1% of an ethoxylated alkylphenol sulfate having a chain of 18 carbon atoms and an average of 13.2moles of ethylene oxide, the ethoxylated sulfate being employed toincrease the brine tolerance of the monoethanolamine C orthoxylenesulfonate surfactant, and 3.4% isopropyl alcohol to reduce the viscosityof the microemulsion.

A 10% PV bank of the foregoing microemulsion was injected into a 4 inchlong Berea core containing residual Loudon crude oil (an oil from theLoudon Field, lllinois) with the microemulsion being driven by a 1000ppm solution of Kelzan XC in Tar Springs Brine for comparative purposes.Severe core plugging was experienced making the microemulsion floodingprocess unsatisfactory. From the flooding test it was determined thatwhen the microemulsion was diluted with the Tar Springs Brine in thepresence of the Kelzan XC, a quite viscous material arose at themultiphase boundary and the multiphase region was encountered almostimmediately, the viscosity of the material being much higher than thatobserved with the brine alone. It is this encountering of the multiphaseregion almost immediately which eliminates the effectiveness of themicroemulsion flooding process in that the miscible displacement of thecrude oil occurs only with the microemulsion being in the single phaseregion. Accordingly, it can be concluded from this comparativeexperiment that the Kelzan XC shows poor phase characteristics with themicroemulsion.

In comparison with the above an example was carried out in accordancewith the present invention in which a PV bank of the same microemulsioncomposition was followed by 8000 ppm Neodol 25-38 in Tar Springs Brine.As a result of such procedure, almost 90% of the crude oil was recoveredand when the oil present in the microemulsion phases was accounted forthe total recovery amounted to 100% of the crude oil and more than halfof the oil injected in the slug. Since no actual formation of two ormore phases was observed with the Neodol 25-38 in the Tar Springs Brinein association with the microemulsion, it is concluded that theexcellent phase behavior attributed to the water-soluble, sulfated,polyethoxylated alcohol in conjunction with the microemulsion providesfor the effective recovery of the crude oil.

Still further, when Tar Springs Brine alone followed by a 5% PV bank ofthe same microemulsion above, the maximum pressure exceeded 35 psi andno appreciable surfactant was produced. When the Neodol 25-38 waspresent in the Tar Springs Brine following the 5% PV slug of themicroemulsion, however, a maximum pressure of 4.9 psi was observed andsurfactant was produced. Also, a lower final oil saturation was achievedin the case of employing the water-soluble, sulfated, polyethoxylatedalcohol in the drive fluid when compared to the case of its absence.This therefore establishes the effectiveness of the water-soluble,sulfated, polyethoxylated alcohol to release entrapped surfactantsthereby improving recovery results.

While the present invention has been described primarily with regard tothe foregoing specific exemplification, it should be understood that thepresent invention cannot under any circumstances be deemed limitedthereto but rather must be construed as boardly as all or anyequivalents thereof.

We claim:

1. In a method of recovering crude oil from a subter ranean formationhaving at least one injection means in fluid communication with at leastone production means wherein a displacing fluid is injected into saidformation through said injection means to displace crude oil toward saidproduction means and said displacing fluid is driven through saidformation by means of a driving fluid, the improvement wherein saiddriving fluid comprises a single phase, transparent, aqueous solution ofa water-soluble, sulfated, polyethoxylated alcohol, said sulfated,polyethoxylated alcohol being present in an amount effective to thickensaid driving fluid, and said driving fluid being substantially free ofany other thickening agent and any other surface active agent.

2. The method of claim 1 wherein said sulfated, polyethoxylated alcoholis a sulfated polyethoxylated C primary alcohol or alkylphenol.

3. The method of claim 2 wherein said sulfated, polyethoxylated alcoholis a sulfated polyethoxylated C primary alcohol.

4. The method of claim 1 wherein said sulfated polyethoxylated alcoholis present in an amount of up to l.5% by weight, based on the weight ofsaid driving fluid.

5. The method of claim 1 wherein said displacing fluid is selected froman aqueous surfactant slug, miscible oil slug and microemulsion slug.

6. The method of claim 5 wherein said displacing fluid is a translucentor transparent, single-phase microemulsion.

7. The method of claim 1 wherein said driving fluid is a brine solutionof said water-soluble, sulfated, polyethoxylated alcohol.

8. The method of claim 1 wherein the injection of said driving fluid anddisplacing fluid is conducted after primary depletion and waterflooding.

9. In a method of recovering oil from a subterranean formation having atleast one injection means in fluid communication with at least oneproduction means wherein said formation has been subjected to primarydepletion and waterflooding and wherein tertiary recovery is carried outby injection of a displacing fluid selected from an aqueous surfactantslug, miscible oil slug, and microemulsion slug and said placing fluidis driven through said formation to displace crude oil toward saidproduction means, the improvement wherein said driving fluid comprises asingle-phase, transparent, aqueous solution of a water-soluble,sulfated, polyethoxylated alcohol, in an amount of up to 1.5% by weightbased on the weight of said driving fluid, and said driving fluid beingsubstantially free of any other thickening agent and any other surfaceactive agent.

10. The method of claim 9 wherein said sulfated, polyethoxylated alcoholis a sulfated polyethoxylated C primary alcohol or alkylphenol.

11. The method of claim 10 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C1245 primary alcohol.

12. The method of claim 9 wherein said displacing fluid is a translucentor transparent, single-phase microemulsion.

13. The method of claim 9 wherein said driving fluid is a brine solutionof said water-soluble, sulfated, polyethoxylated alcohol.

14. A method of recovering crude oil from a subterranean formationhaving at least one injection means in fluid communication with at leastone production means which comprises:

injecting into said formation through said injection means a displacingfluid capable of displacing crude oil in said formation toward saidproduction means;

injecting into said formation through said injection means a drivingfluid comprising a single-phase, transparent aqueous solution of awater-soluble, sulfated polyethoxylated alcohol, to drive saiddisplacing fluid and displaced crude oil toward said production means,said driving fluid being substantially free of any other thickeningagent and any other surface active agent; and

recovering displaced crude oil through said production means.

15. The method of claim 14 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C primary alcohol or alkylphenol.

16. The method of claim 15 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C1245 primary alcohol.

17. The method of claim 16 wherein said sulfated polyethoxylated alcoholis present in an amount of up to l.5% by weight, based on the weight ofsaid driving fluid.

18. The method of claim 14 wherein said displacing fluid is selectedfrom an aqueous surfactant slug, miscible oil slug, and microemulsionslug.

19. The method of claim 18 wherein said displacing fluid is atranslucent or transparent, single-phase microemulsion.

20. The method of claim 14 wherein said driving fluid is a brinesolution of said water-soluble, sulfated, polyethoxylated alcohol.

21. A method of recovering crude oil from a subterranean formationhaving at least one injection means in fluid communication with at leastone production means which comprises:

injecting into said formation through said injection means amicroemulsion slug to displace crude oil toward said production means;

injecting into said formation through said injection means a drivingfluid comprising a single-phase, transparent, aqueous solution of awatersoluble, sulfated, polyethoxylated alcohol in an amount of up to1.5% by weight, based on the weight of said driving fluid, to drive saidmicroemulsion and displaced crude oil toward said production means, saiddriving fluid being substantially free of any other thickening agent andany other surface active agent; and

recovering displaced crude oil through said production means.

22. The method of claim 21 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C primary alcohol or alkylphenol.

23. The method of claim 22 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C1245 primary alcohol.

24. The method of claim 21 wherein said driving fluid is a brinesolution of said water-soluble, sulfated, polyethoxylated alcohol.

25. The method of claim 21 wherein the injection of said driving fluidand displacing fluid is conducted after primary depletion andwaterflooding.

1. IN A METHOD OF RECOVERING CRUDE OIL FROM A SUBTERRANEAN FORMATIONHAVING AT LEAST ONE INJECTION MEANS IN FLUID COMMUNICATION WITH AT LEASTONE PRODUCTION MEANS WHEREIN A DISPLACING FLUID IS INJECTED INTO SAIDFORMATION THROUGH SAID INJECTION MEANS TO DISPLACE CRUDE OIL TOWARD SAIDPRODUCTIN MEANS AND SAID DISPLACING FLUID IS DRIVEN THROUGH SAIDFORMATION BY MEANS OF A DRIVING FLUID, THE IMPROVEMENT WHEREIN SAIDDRIVING FLUID COMPRISES A SINGLE PHASE, TRANSPARENT, AQUEOUS SOLUTION OFA WATER-SOLUBLE, SULFATED, POLYETHOXYLATED ALCOHOL, SAID SULFATED.POLYETHOXYLATED ALCOHOL BEING PRESENT IN AN AMOUNT EFFECTIVE TO THICKENSAID DRIVING FLUID, AND SAID DRIVING FLUID BEING SUBSTANTIALLY FREE OFANY OTHER THICKENING AGENT AND ANY OTHER SURFACE ACTIVE AGENT.
 2. Themethod of claim 1 wherein said sulfated, polyethoxylated alcohol is asulfated polyethoxylated C10-18 primary alcohol or alkylphenol.
 3. Themethod of claim 2 wherein said sulfated, polyethoxylated alcohol is asulfated polyethoxylated C12-15 primary alcohol.
 4. The method of claim1 wherein said sulfated polyethoxylated alcohol is present in an amountof up to 1.5% by weight, based on the weight of said driving fluid. 5.The method of claim 1 wherein said displacing fluid is selected from anaqueous surfactant slug, miscible oil slug and microemulsion slug. 6.The method of claim 5 wherein said displacing fluid is a translucent ortransparent, single-phase microemulsion.
 7. The method of claim 1wherein said driving fluid is a brine solution of said water-soluble,sulfated, polyethoxylated alcohol.
 8. The method of claim 1 wherein theinjection of said driving fluid and displacing fluid is conducted afterprimary depletion and waterflooding.
 9. In a method of recovering oilfrom a subterranean formation having at least one injection means influid communication with at least one production means wherein saidformation has been subjected to primary depletion and waterflooding andwherein tertiary recovery is carried out by injection of a displacingfluid selected from an aqueous surfactant slug, miscible oil slug, andmicroemulsion slug and said placing fluid is driven through saidformation to displace crude oil toward said production means, theimprovement wherein said driving fluid comprises a single-phase,transparent, aqueous solution of a water-soluble, sulfated,polyethoxylated alcohol, in an amount of up to 1.5% by weight based onthe weight of saId driving fluid, and said driving fluid beingsubstantially free of any other thickening agent and any other surfaceactive agent.
 10. The method of claim 9 wherein said sulfated,polyethoxylated alcohol is a sulfated polyethoxylated C10-18 primaryalcohol or alkylphenol.
 11. The method of claim 10 wherein saidsulfated, polyethoxylated alcohol is a sulfated polyethoxylated C12-15primary alcohol.
 12. The method of claim 9 wherein said displacing fluidis a translucent or transparent, single-phase microemulsion.
 13. Themethod of claim 9 wherein said driving fluid is a brine solution of saidwater-soluble, sulfated, polyethoxylated alcohol.
 14. A method ofrecovering crude oil from a subterranean formation having at least oneinjection means in fluid communication with at least one productionmeans which comprises: injecting into said formation through saidinjection means a displacing fluid capable of displacing crude oil insaid formation toward said production means; injecting into saidformation through said injection means a driving fluid comprising asingle-phase, transparent aqueous solution of a water-soluble, sulfatedpolyethoxylated alcohol, to drive said displacing fluid and displacedcrude oil toward said production means, said driving fluid beingsubstantially free of any other thickening agent and any other surfaceactive agent; and recovering displaced crude oil through said productionmeans.
 15. The method of claim 14 wherein said sulfated, polyethoxylatedalcohol is a sulfated polyethoxylated C10-18 primary alcohol oralkylphenol.
 16. The method of claim 15 wherein said sulfated,polyethoxylated alcohol is a sulfated polyethoxylated C12-15 primaryalcohol.
 17. The method of claim 16 wherein said sulfatedpolyethoxylated alcohol is present in an amount of up to 1.5% by weight,based on the weight of said driving fluid.
 18. The method of claim 14wherein said displacing fluid is selected from an aqueous surfactantslug, miscible oil slug, and microemulsion slug.
 19. The method of claim18 wherein said displacing fluid is a translucent or transparent,single-phase microemulsion.
 20. The method of claim 14 wherein saiddriving fluid is a brine solution of said water-soluble, sulfated,polyethoxylated alcohol.
 21. A method of recovering crude oil from asubterranean formation having at least one injection means in fluidcommunication with at least one production means which comprises:injecting into said formation through said injection means amicroemulsion slug to displace crude oil toward said production means;injecting into said formation through said injection means a drivingfluid comprising a single-phase, transparent, aqueous solution of awatersoluble, sulfated, polyethoxylated alcohol in an amount of up to1.5% by weight, based on the weight of said driving fluid, to drive saidmicroemulsion and displaced crude oil toward said production means, saiddriving fluid being substantially free of any other thickening agent andany other surface active agent; and recovering displaced crude oilthrough said production means.
 22. The method of claim 21 wherein saidsulfated, polyethoxylated alcohol is a sulfated polyethoxylated C10-18primary alcohol or alkylphenol.
 23. The method of claim 22 wherein saidsulfated, polyethoxylated alcohol is a sulfated polyethoxylated C12-15primary alcohol.
 24. The method of claim 21 wherein said driving fluidis a brine solution of said water-soluble, sulfated, polyethoxylatedalcohol.
 25. The method of claim 21 wherein the injection of saiddriving fluid and displacing fluid is conducted after primary depletionand waterflooding.